Fentanyl (CAS Registry No. 437-38-7) N-phenyl-N-[1-(2-phenyl-ethyl)-4-piperidinyl]propanamide and its salts, in particular its citrate salt (CAS Registry No. 990-73-8) are opiates, controlled substances, and extremely potent narcotic analgesics. Fentanyl and its citrate salt are currently marketed by a number of companies in a number of delivery formats. Fentanyl citrate, for example, is available as an injectable and an oral lozenge on a stick, the latter sold under the trade name ACTIQ. Three patents are identified in the FDA publication Approved Drug Products With Therapeutic Equivalence Evaluations (hereinafter “the Orange Book”) as relating to ACTIQ: U.S. Pat. Nos. 4,671,953, 4,863,737 and 5,785,989. A second form of ACTIQ may also be available. This form may be a compressed tablet on a stick. Like the original ACTIQ lozenge, this second form is believed to exhibit the same disintegration rate, Tmax, Cmax and AUC as the original lozenge. Accordingly, they will be discussed collectively, except where expressly stated otherwise or as the context dictates.
A review of the package insert information for ACTIQ sold by Cephalon, Inc., 145 Brandy Wine Parkway West, Chester, Pa. 19380, available in the Physician's Desk Reference, 57th ed. 2003 at page 1184, brings instant perspective on the seriousness of the afflictions of the patients who take it. According to its label, ACTIQ “is indicated only for the management of break-through cancer pain in patients with malignancies who are already receiving and who are tolerant to opiate therapy for their underlying persistent cancer pain.” (Id., emphasis in original). The text of the ACTIQ label is hereby incorporated by reference.
In clinical trials of ACTIQ, breakthrough cancer pain was defined as a transient flare of moderate-to-severe pain occurring in cancer patients experiencing persistent cancer pain otherwise controlled with maintenance doses of opiate medications, including at least 60 mg of morphine/day, 50 micrograms transdermal fentanyl/hour or equianalgesic dose of another opiate for a week or longer. Thus patients receiving ACTIQ are patients with suddenly intolerable pain, which flares up despite undergoing chronic analgesic treatment. Providing pain relief from such breakthrough pain is inexorably linked with the patient's immediate quality of life. And for such patients, providing breakthrough pain relief may be the only thing that medical science can offer.
As with many things in medicine, there is always room for improvement. Fentanyl is an expensive drug, costing manufacturers as much as $100/gram or more. While cost is by no means an overriding issue, the cost of medication is an issue to be considered. A formulation that allows for a reduction in the amount of fentanyl could reduce the overall cost of a patient's care.
Far more importantly, a reduction in dose of such a potent opiate while still achieving beneficial management of breakthrough pain in cancer patients, has very far reaching and desirable consequences in terms of patients overall care. Opiate mu-receptor agonists, including fentanyl, produce dose dependent respiratory depression. Serious or fatal respiratory depression can occur, even at recommended doses, in vulnerable individuals. As with other potent opiates, fentanyl has been associated with cases of serious and fatal respiratory depression in opiate non-tolerant individuals. Thus, the initial dose of ACTIQ used to treat episodes of breakthrough cancer patients should be 200 micrograms and each patient should be individually titrated to provide adequate analgesia while minimizing side effects. And the side effects, even those that are not life threatening, can be significant.
In addition, fentanyl, as a mu-opiate agonist can produce drug dependence and tolerance. Drug dependence in and of itself is not necessarily a problem with these types of cancer patients. But, fentanyl can be used in the treatment of other types of pain as well. In such treatment protocols, dependence and tolerance may be significant issues. Moreover, cancer patients are generally undergoing heavy medication. The longer that a lower dose of medication can be provided, the better.
U.S. Pat. No. 6,200,604 (“the '604 patent”), which issued Mar. 13, 2001 to CIMA LABS INC., 10000 Valley View Road, Eden Prairie, Minn. 55344, exemplifies two fentanyl formulations each containing 36% effervescents and 1.57 milligrams of fentanyl citrate. See example I thereof, col. 5, ln. 60 through col. 6, ln. 30. The '604 patent describes the use of, amongst other things, effervescence as a penetration enhancer for influencing oral drug absorption. See also U.S. Pat. Nos. 6,759,059 and 6,680,071. See also Brendenberg, S., 2003 New Concepts in Administration of Drugs in Tablet Form: Formulation and Evaluation of a Sublingual Tablet for Rapid Absorption, and Presentation of an Individualized Dose Administration System, Acta Universitiatis Upsaliensis. Comprehensive Summaries of Uppsala Dissertations from the Faculty of Pharmacy, 287, 83 pp. Uppsala ISBN 91-554-5600-6.
If lower doses of fentanyl which nonetheless provide similar pain relief could be achieved, patients could obtain comparable benefit with much less drug at lower cost and with a reduced risk of side effects. Thus, improvement in the administration of fentanyl is still desirable.